Radio Frequency Identification (RFID) tags are widely used for automatic time and/or location registration systems in sporting events. Typically an RFID tag comprises a microchip combined with an antenna and is structured to allow attachment to an object to be detected. In such time registration systems every participant is provided with an RFID tag, which is removable secured to a shoe or a bib comprising a number, which is associated with the name and/or address of the participant. If a participant crosses a detection antenna an electro-magnetical coupling between the tag and the antenna is established thereby allowing information exchange, e.g. an identify number associated with the tag, between the tag and a detector connected to the antenna.
Currently there is a development towards the use of so-called ultra-high frequency (UHF) tags, which use frequency in the UHF band between approximately 860 and 960 MHz. These tags are much cheaper (so that they can be used as a one-time use disposable tag), are less in weight, and can be read faster and from larger distances when compared with low frequency tags. From a logistic and organisational point of view, tags are preferably distributed together with or attached to the bib so that there is an unambiguous one-to-one relation between the tag and the bib. The bib is fixed to the shirt such that the bib is located in front of the chest of the participant.
When fixing an UHF tag to a bib certain problems occur. One problem relates to the fact that the tag is within close proximity of the body, which for the tag functions as a dielectric of relatively high dielectric constant. The proximity of the body changes the impedance of the tag antenna thereby “detuning” the tag away from its optimum working point. Due to this detuning effect, the tag may not able to generate detectable modulated backscatter signal. The effect of detuning is further enhanced in a wet environment, e.g. wet and sweaty clothing and/or body of an athlete. This way, the signal may further deteriorate thereby increasing the risk that a participant crossing or passing a detection antenna is not or at least not correctly registered by the timing system.
In order to lift at least part of this problem, a spacer in the vicinity of the tag may be used such that at least a certain distance between the tag and the wet clothes and/or body is provided. Such spacer may have the form of a strip of lightweight foam attached to or in the vicinity of the tag. Ideally such spacer should guarantee a spacing distance of about 10 mm, however such thickness makes such tag bib assemblies not suitable for mass distribution (by post) and storage (e.g. millions or more). Therefore, in practice, spacers are used which are thinner than the desirable optimal thickness. Hence, conventional spacers thus allow only sub-optimal performance of the tag.
A further problem associated with the use of a tag bib assembly is that the tag signal may be influenced by nearby objects. Especially when a lot of participants are crossing an antenna simultaneously, the presence of other persons in the direct proximity of the radiated signal may cause that only a very small part of the signal will be picked up by the detection antenna of the timing system. Hence, when using a tag bib assembly, it is desired that the tag signal is directed towards the detection antenna.
U.S. Pat. No. 7,948,383 describes an RFID tag assembly for a shoe. In particular, the tag is removed from a bib and secured to a participant's shoe prior to a race. Attaching the RFID tag to the shoe requires multiple actions of the user. Improper installation of the tag to the shoe may result in a disfunctioning or even a non-functioning tag.
Accordingly, there is a need to provide an improved tag assembly, which at least alleviates at least part of these problems. In particular, there is a need for improved tag bib assemblies, in particular UHF tag bib assemblies, which are suitable for fixing to the shirt of a participant and which are not or much less affected by the wet clothes and/or body of the participant. Further, there is a need for improved tag bib assemblies, which allow the generation of a signal, which is focussed towards the detection antenna.